SCHIEFFER: Today on FACE THE NATION, America on edge as the U.S. government issues a worldwide terror alert. Twenty-two U.S. embassies are closed because officials say they've uncovered a possible terror threat from al Qaeda. We'll have reports on that and get the latest from the chairman of the House Homeland Security Committee, Michael McCaul. Then we'll turn to the week's other big story: the fallout from Russia granting asylum to NSA leaker Edward Snowden.

SEN. CHARLES SCHUMER: Russia has stabbed us in the back. And each day that Snowden is allowed to roam free is another twist of the knife.

SCHIEFFER: We'll hear from New York Democrat Chuck Schumer. And we'll talk with House Budget Committee Chairman Paul Ryan. Plus analysis from The Washington Post's Dan Balz, author of the new book "Collision 2012." Peggy Noonan of The Wall Street Journal. Barton Gellman of TIME magazine and The Washington Post. David Sanger of The New York Times. And CBS News political director John Dickerson. A lot to cover, but it's what we do on FACE THE NATION.

ANNOUNCER: From CBS News in Washington, FACE THE NATION with Bob Schieffer.

SCHIEFFER: And good morning again. Well, we're getting more detail this morning on why the government has closed those 22 American diplomatic posts across the Mideast and North Africa, and why they are taking so seriously the threat of a possible al Qaeda attack. The travel warning that the State Department issued last week for Americans traveling overseas we're now told will remain in effect for the rest of this month. For the latest this morning, we're going to our CBS News homeland security correspondent Bob Orr, who has been all on this for -- oh, for a long, long time. Bob, why are they taking this one so much more seriously than some of the things in the past?

BOB ORR, CBS HOMELAND SECURITY CORRESPONDENT: Because this threat, Bob, comes from the group from al Qaeda, al Qaeda in the Arabian Peninsula and Yemen. It has been the most dedicated, the most active, and is charged from al Qaeda leadership with being in charge of attacking Americans. This is a serious, credible threat, probably the most serious the government has seen since 2006. The problem here is while we know a great deal about what they're trying to do, we're missing some very important points: the date, the time, the scope of the attack, intelligence working overtime this weekend trying to get some of those factors nailed down so that we can try to disrupt this plot.

SCHIEFFER: But there's a lot of really scary stuff going on this morning, talking about surgically-inserted bombs, for one thing. They seem to be talking about something they describe as big.

ORR: Yes, I think the fear is that this may be a big play from a group that has been unable to muster a large-scale attack since 9/11. And they've got some expertise. You talk about the scary stuff. They have a bomb-maker in Yemen named Ibrahim al-Asiri. He is the guy that built the underwear bombs and the printer cartridge bombs. He's a devious genius. And we know in the past he has experimented in research trying to build body bombs, that is, implant explosives in human beings which would give a whole new meaning to suicide bombers. Now while we're not certain at all that that's part of this threat, the fact is he's part of the brain trust there in Yemen that has been working on plots and it can't be discounted. I think what they're really worried about here is something on the scale of like a Mumbai-style ground-based attack that could use explosives and arms. But, again, this is all very fuzzy because the partial information is based on intercepts that the government heard, major al Qaeda figures talking to one another. And that's not real specific.

SCHIEFFER: There have been a number of al Qaeda escapees recently, especially from places like Libya. Do we think there's any connection between that and this?

ORR: Well, it's possible. There was a big prison break in Libya. There was a big prison break in Iraq. This is a lot of manpower for an organization that has been somewhat diminished. But there are some other markers too, Bob. This week Ayman al- Zawahiri, the leader of al Qaeda, had two messages. One came out earlier in the week saying: "It's time again to attack the Americans." And he wanted to free the prisoners in Guantanamo. And then he called for more unrest in Egypt. In the past when the leader of al Qaeda has come out with public messages, that has sometimes been a "go "signal for operators on the ground. Our colleague John Miller has been told there are already operatives in place. And our government knows that much but we don't know where and we don't know what the target is.

SCHIEFFER: OK. Thank you very much, Bob. And we want to go directly now to CBS News foreign correspondent Clarissa Ward, who is at the U.S. embassy in Cairo, which is closed this morning, and where this latest al Qaeda threat just adds to the very tense situation there. Clarissa, what's the latest?

CLARISSA WARD, CBS FOREIGN CORRESPONDENT: Good morning, Bob. Well, the U.S. embassy here in Cairo is just about 200 yards behind me. You can probably see that blast wall there which cuts off any traffic from getting any closer to the embassy. Security is always very tight here, but today the embassy is closed, along with every single other U.S. embassy in the Arab world, as well as several others in predominantly Muslim countries. Now, it's not just diplomats who are being affected here. CBS News has confirmed at least one other U.S. non-governmental organization has asked its American employees to stay at home and work from home today. The period of concern appears to be these final few days of the Muslim holy month of Ramadan. This is one of the most important times in the Muslim calendar. And it is expected all these embassies will open again tomorrow, Bob, but the State Department has said that there may be further closures in the future as it assesses that threat.